Swiss mathematician and physicist. In 1926 Stueckelberg got his Ph.D. at Munich under Arnold Sommerfeld. He qualified as a university lecturer together with Konrad Bleuler under supervison from Gregor Wentzel at the University of Zürich. Stueckelberg became then Assistant Professor at Princeton University.

In 1934 he devised a fully covariant perturbation theory for quantum fields. To quote a paper of Lacki et al., "The approach proposed by Stueckelberg was far more powerful, but was not adopted by others at the time". It still has not been. However, besides being explicitly covariant, Stueckelberg's methods avoid vacuum bubbles.

Independently from Hideki Yukawa, and arguably before him, he gave vector boson exchange as the theoretical explanation of the strong nuclear force in 1935.

The evolution parameter theory he presented in 1941 and 1942 is the basis for recent work in Relativistic dynamics.

In 1942 he proposed the interpretation of the positron as a negative energy electron traveling backward in time.This result was quoted by Feynmamnn in the abstract of his classic paper: “The theory of Positrons”, Phys. Rev.76, 749-759 (1949).

In 1943 he came up with a renormalization program to attack the problems of infinities in quantum electrodynamics (QED), but his paper was rejected by the Physical Review. In 1976 he was awarded the Max Planck medal.